Sensors built into the vehicle fender are used to detect accidents involving pedestrians. Systems based on two or more acceleration sensors are common.
Recently available are systems based on a pressure tube for detecting accidents involving pedestrians.
Both for the acceleration-based systems and for the pressure-tube-based systems, the impact of an object in the relevant region of the fender results in a signal rise inside the detecting sensors.
The amplitude of the detected signals depends, amongst other factors, on the mass and speed of impact of the object involved in the impact.
Nowadays either pressure sensors or acceleration sensors are used for detecting collisions to the side. Acceleration sensors are typically located on the B-pillar, C-pillar or D-pillar of the vehicle. Pressure sensors are typically arranged in the vehicle door.
Acceleration sensors are used today for detecting frontal collisions. These sensors are typically located at a control unit arranged in the center of the vehicle and are also located along the bending crossmember of the vehicle.
The signals output by the sensors undergo further processing by procedures performed by the control unit. If the procedure ascertains from the signals a pedestrian being hit, a lateral collision or a frontal collision, then restraining means (e.g. an airbag) are activated in the vehicle according to the processing result from the procedure in order to protect the pedestrian in the event that a pedestrian is hit, or, in the event of a collision, to protect the vehicle occupants.
There are a vast range of transmission standards available for transmitting the signals from the sensors used. One of these standards is the standard based on the Peripheral Serial Interface 5 (PSI5).
PSI5 is an open standard initiated by the companies Autoliv, Robert Bosch GmbH and Continental AG. Based on the earlier PAS4 protocol, PSI5 supports applications in which it is possible to poll up to 4 sensors per bus node in various configurations. There is also provision for bidirectional communication for the purpose of sensor configuration and diagnostics.
In airbag systems, data from pressure sensors and acceleration sensors, for example, is evaluated via current-modulated two-wire bus lines, which use a Manchester-coded protocol to communicate with the control unit.
The standard also specifies a plurality of operating modes. These are classified primarily into synchronous and asynchronous operating modes. For synchronous operation, the following three operating modes are defined according to how the sensors are connected to the control unit: Parallel BUS mode (all the sensors are connected in parallel), Universal BUS mode (sensors connected in series) and Daisy Chain BUS mode. Combined with other parameters such as the total number of communication slots, data rate, data word length, parity/CRC monitoring, the PSI5 standard allows a range of implementation options. The 10-bit data word length is widely used.
Sensors used today that transmit measured values according to the PSI5 standard typically use a single PSI5 communication slot for data transmission of the measured values to a receiver, for instance to a control unit. This means that such a sensor communicates in a single PSI5 communication slot within a PSI communication bus. Exceptions are two-channel sensors, where the measured values from one sensor detection means (for instance X-direction) are transmitted on one channel, while the measured values from another sensor detection means (for instance Y-direction) are transmitted on a second channel. In this case, the corresponding sensor needs more current for data transmission, and, for example, there is a greater temperature rise inside the sensor. Such sensors must have a suitable structural design in order to dissipate the resulting thermal load reliably via the sensor housing, for instance. This potentially results in increased costs.